1. Technical Field
The present invention relates to an image forming apparatus and an image forming system which performs halftoning by using a dither matrix.
2. Description of the Related Art
In a known image forming apparatus of an electrophotographic type, an electrically charged photoconductor drum is irradiated with a light source such as a laser and the voltage of a corresponding portion of the photoconductor drum is changed to cause toner to adhere thereto. Then, a toner image formed on the photoconductor drum is transferred to a printing paper by a transfer roller applied with a voltage opposite from the photoconductor drum. Thereafter, a fixing roller fixes the toner with heat and pressure. Accordingly, a printing result is obtained on the printing paper.
Here, in order to express tones of an image artificially, there is a case such that a halftoning using a dither matrix is performed. By the halftoning, for example, input image data of 256 tones is converted into two-tone output image data, and an image is formed on the basis of the output image data, so that dots of a size according to the tone are arranged discretely at regular pitches, whereby an image in which the tone is artificially reproduced is formed.
However, when the photoconductor drum is driven by a drum gear, a drive force from a drive motor is transmitted to the photoconductor drum via a drive gear and the above-described drum gear engaging therewith. In this configuration, when the drive gear and the drum gear engage, the uneven rotation occurs. It may causes that the pitches of the dots discretely arranged and the cycle of uneven rotation get closer as a result of the halftoning, interference may occur between them, and interference fringes (variable density in the image) may be generated.